A man deported earlier this year was regarded by gardaí and military intelligence as a major target here and was under regular monitoring and surveillance.

His arrest and removal from Ireland was seen as very significant from a domestic security perspective.

He was deported by immigration authorities after he was found to have taken part in a sham marriage.

According to Garda officers, he had a number of international connections to people on watch lists drawn up by other police forces.

He was regarded as playing a key role in providing logistical support for terrorists.

The man was arrested by officers from the Garda National Immigration Bureau under Operation Vantage, which was set up in 2015 to tackle the growing racket in marriages of convenience.

Vantage was established after officers noted a huge increase in the number of asylum applications and sham marriages.

Suspicions

The sham marriages had flourished initially because of a loophole in the law, created after the High Court struck down legislation, which had previously allowed gardaí to combat abuses.

But a new law, introduced by then justice minister Frances Fitzgerald, gave widespread powers to registrars to investigate a planned marriage, if suspicions had been aroused.

On Saturday, the Irish Independent revealed more than 70 jihadi sympathisers are now being closely monitored here by Garda anti-terrorist units and military intelligence.

The network of suspects has grown as the two organisations step up physical and technical surveillance of those providing logistical support for Islamist activists based elsewhere in Europe.

The top tier involves between 20 and 30 sympathisers, who are providing logistical support here, such as providing false documentation and identity papers.

The threat level in this country from international terrorists remains at moderate, which means an attack is possible but not likely. The level was raised from low to moderate after the Charlie Hebdo attack in Paris in January 2015.